Some fabric treatment appliances, such as a washing machine, a clothes dryer, and a fabric refreshing or revitalizing machine, use steam generators for various reasons. The steam from the steam generator may be used to, for example, heat water, heat a load of fabric items and any water absorbed by the fabric items, dewrinkle fabric items, remove odors from fabric items, sanitize the fabric items, and sanitize components of the fabric treatment appliance.
Water from a water supply coupled with the steam generator typically provides water to the steam generator for conversion to steam. The water supply fills a steam generation chamber of the steam generator with water, and a heating element of the steam generator is activated to heat the water present in the steam generation chamber to generate steam. Steam generated in the steam generation chamber commonly flows from the steam generation chamber to a fabric treatment chamber via a steam supply conduit attached to the steam generator.
One problem associated with steam generators, especially in-line or flow-through steam generators, is that the heating element distributes heat in an inefficient manner. The heating element wraps around the steam generator in a manner providing, by conduction through the steam generator, substantially uniform thermal output into the steam generation chamber. For example, a standard in-line steam generator has a heating element formed from a resistive wire that is wrapped around the steam generation chamber. The steam generation chamber is often filled with an operating volume of water less than the total capacity of the steam generation chamber to provide for faster steam generation times and to provide room for expansion and boiling water. The operation volume of water results in an operational water level within the steam generation chamber. Air fills the steam generation chamber above the operational water level. However, the heating element is wrapped around the portion of the steam chamber containing both water and air. As the air is not a good conductor of heat, the portion of the heating element below the water level will more efficiently conduct heat into the water than the portion of the heating element above the water level.
In addition, inefficient heating of the steam generator can increase the buildup of scale inside the steam generation chamber. The temperature of the water in the steam generation chamber is limited, as it will eventually change phase to steam when it receives enough thermal output. The temperature of the steam, air, and vapor, however, is not limited. The upper portion of the steam generation chamber, therefore, has a tendency to reach higher temperatures. Higher temperatures convert soft calcium deposits in the steam generation chamber to hard calcium, which is not easily removed by the movement of water therein. If flow out of the steam generator or flow through the steam supply conduit becomes impaired due to the buildup of scale, the steam generator will malfunction and possibly damage the fabric treatment appliance.